The present invention relates to a slot machine which preselects a prize-winning combination of symbols based on a random-sampled number and controls a plurality of lengthwise movable series of symbols to stop so as to provide the preselected prize-winning combination of symbols on a winning line.
Slot machines have heretofore been controlled to pay out coins with a definite pay-out ratio being maintained at a predetermined level, and have been adapted to preselect an occurrence of a prize-winning combination of symbols and the pay-out value of the prize-winning combination of symbols, both based on a random-sampled number from a predetermined series of random numbers, so as to avoid prize-winning combinations of symbols occurring with different frequencies according to the skill of players.
In such the slot machine having, for example, three symbols reels, a random-sampled number is referred to values of a probability table so as to predetermined the pay-out value of a combination of symbols to be selected, according to which an appropriate combination of symbols is selected with reference to symbol tables associated with the respective reels. Alternatively, each symbol on each reel corresponds to a single random number so as to be unconditionally specified by sampling one of a series of random numbers.
In most slot machines wherein a symbol to be selected on a winning line is determined by sampling a random number for each reel, there is a difference in number between the series of random numbers and the symbols on the reels. A series of random numbers generated from, for example, a 15-bit register is 32,768 in number in the binary system of notation, while there are, if each reel has 22 symbols, 10,648 possible combinations of symbols to be selected. Therefore, there will be a difference in probability between the occurrence of any one of the possible combinations of symbols and the sampling of a specific random number corresponding to the combination of symbols to be produced. As a result, even if a random number can be sampled with uniform probability, the selection of a combination of symbols will have a weight probability which is undesirable in such games.
This weighted probability can be theoretically eliminated by the provision of random numbers of the same number as the possible combinations of symbols. However, since an n-bit register is ordinarily used in a random number generator, the random number generator is very complicated in circuitry and the generation of random numbers would be very difficult in the case of generating the same number of random numbers as the number of possible combinations of symbols on the reels.